Since Zoolock came to prominence, a large number of variations have cropped up. Each subsequent variation has grown the deck's size and cost, as each try to solve various problems that crop up with the meta.
Reynad's ZoolockZoolock first came to prominence around mid-March 2014 via Reynad. At the time he proclaimed it the best deck in Hearthstone. And at the time he was right. There were no counters to the deck, and it maintained an over 70% win-rate in high level play. And even as the counters started to appear, the deck was still difficult to beat, even when it didn't draw into the perfect curve turn after turn.
The original Zoolock is a tight, cheap deck. One of the reasons why it became popular is its ability to win and its inexpensive card cost; it uses no legendaries or epics and costs only 1480 dust (less than the cost of one legendary).
This is still the Zoolock deck I use more often than not. It's the cleanest and surest implementation. Whereas it can suffer in very control-oriented metas, its win-rate still doesn't drop below 50%.
For the following decks I'll list how their builds differ from the original Reynad Zoolock, and then give my own analysis of the deck based on play in the early July season ranked meta.
Trump's ZoolockDifferences: -2 Mortal Coil, -2 Shieldbearer, -2 Young Priestess, -1 Argent Commander, +2 Abusive Sergeant, +1 Elven Archer, +2 Blood Knight, +2 Dark Iron Dwarf
I find this to be the weakest of the variants I examine. It mainly tries to counter control decks by enabling stronger trades through attack boosts via Dark Iron Dwarf and Abusive Sergeant, while also giving larger board presence via possible Blood Knight synergy.
What I find weakest about this deck are the two Blood Knights. First of all, there's an urge to keep Blood Knight in hand until you can get the value from the card, which means a dead card in hand. Oft times, you're simply forced to play Blood Knight without its battlecry. One Blood Knight that doesn't get value is inefficient, but two really weaken the deck.
I also find the Elven Archer an odd choice in the deck, especially without including Amani Berserker. A 1 mana 1/1 is weak board presence, even with its one additional battlecry damage. I favour Mortal Coil in this instance, since you can often get the value for the additional card draw. I would personally rather have the card draw than the additional 1/1 on the board.
Flood's ZoolockDifferences: -2 Mortal Coil, -2 Shieldbearer, -2 Harvest Golem, -2 Scarlet Crusader, -2 Shattered Sun Cleric, +2 Abusive Sergeant, +2 Elven Archer, +2 Amani Berserker, +1 Blood Knight, +1 King Mukla, +2 Dark Iron Dwarf
I find this deck to be a stronger variation of what the Trump deck is trying to do. Elven Archer synergy with Amani Berserker means more powerful damage to the opponent's face in aggro matchups or better ability to control the board against control and mid-range decks. An early King Mukla is a strong play against most every matchup except aggro (and especially weak against Paladin aggro). I find it's easier to get value from a single Blood Knight, and it's not as detrimental to hold it back until that advantage can be gained (although the loss of the Scarlet Crusaders impacts this somewhat).
I play this deck reasonably often when the meta is more oriented towards control. I do find this weaker against aggro matchups than Reynad's original Zoolock, but not so much that it's advantages against control will tank win percentages across the board.
Alchemixt's ZoolockDifferences: -2 Mortal Coil, -2 Shieldbearer, -1 Dire Wolf Alpha, -2 Scarlet Crusader, -2 Shattered Sun Cleric, -1 Argent Commander, +1 Power Overwhelming, +2 Abusive Sergeant, +2 Leper Gnome, +1 Amani Berserker, +1 Big Game Hunter, +1 Dark Iron Dwarf, +1 Leeroy Jenkins, +1 The Black Knight
This is mainly a tournament deck, meant to offer tools to get around many of the strengths of a control deck. Control being popular in tournament, you can't ignore it when building an aggro deck. The inclusion of Big Game Hunter and The Black Knight can get you past those mid- to late-game taunts and threats.
This deck just doesn't work on ladder. You don't see enough consecutive control matchups to make this worthwhile overall. This deck is exceptionally weak in aggro matchups. It's a much slower version of the other Zoolock decks examined. It's also weaker versus mid-range decks, an archetype that Zoolock generally shines against.
I included this deck in my examinations to illustrate that a strong tournament deck (and this did get Alchemixt to a Hearth Wars season final) does not always translate successfully to ladder play. The reason being that you can always expect certain deck archetypes in tournament (control being the most popular) whereas in ladder you're always facing a variety of deck archetypes.